1. Field of the Invention
The present invention relates to an image pickup device and method for acquiring a synthesized image based on a normal image acquired by irradiating a test object with visible light and a special image acquired by irradiating the test object with special light in a camera for medical use or industrial use, for example.
2. Description of the Related Art
In the related art, for example, an endoscope system for observing a tissue in a body cavity is widely known. An electronic endoscope system for picking up an image of a portion to be observed in the body cavity through irradiation of white light to obtain a normal image and displaying the obtained normal image on a monitor screen has been widely put into practical use.
As the endoscope system described above, the following fluorescent endoscope system has been widely put into practical use. Specifically, the fluorescent endoscope system picks up an autofluorescent image emitted from the portion to be observed through irradiation of excitation light along with the normal image, appropriately synthesizes the normal image and the autofluorescent image, and displays the obtained synthesized image on the monitor screen.
In particular, fluorescence observation in a vascular flow or diseased tissue through the intravenous administration of indocyanine green (ICG) is conventionally performed. It is generally known that fluorescence in the range of 830 nm to 840 nm is obtained with respect to irradiation of excitation light in the range of 750 nm to 790 nm. However, the fluorescence has a wavelength band in a near-infrared range. Therefore, an image obtained in the above-mentioned case is a monochrome image. In addition, in this state, visible portions are not simultaneously visible. Thus, some experiences and intuition are required for the observation and diagnosis on the characteristic blood-flow fluorescent image and diseased tissue in a sentinel lymph node.
In view of the situations described above, the following is proposed in a fluorescent endoscope system described in Japanese Patent Application Laid-open No. 2007-75198. Specifically, the normal image (illumination-light image) and the white-light image (fluorescent image) are synthesized to display the obtained synthesized image on the monitor screen.
As in the case of the fluorescent endoscope system described in Japanese Patent Application Laid-open No. 2007-75198, however, the illumination-light image which is a visible-light image and the fluorescent image are simply synthesized at a predetermined brightness ratio. Therefore, characteristic information to be obtained from the fluorescent image is not appropriately obtained. In addition, the synthesized image contains a large amount of unnecessary information. For example, a blood-flow portion emits autofluorescent light by an excitation-light source through the administration of indocyanine green (ICG). At this time, as a result of reflection of the autofluorescence wavelength light by a peripheral area of the blood-flow portion, even a portion other than the blood-flow portion frequently looks as if the portion emits fluorescent light. Therefore, the obtained synthesized image has low visibility because not only a desired specific portion is not clearly displayed but also even an unnecessary portion is displayed.